July 2015

On the fringes

2011 is coming to an end, which means we're halfway through the Arctic winter. The sea ice is thickening up nicely everywhere in the Arctic interior, but things aren't progressing as uniformly at the edges. Just like last year we see an above average ice cover in some regions, but a very slow freeze-up in other regions.

A good example of the former is Hudson Bay. It was extremely late in freezing over last year, and thus melted very fast in Spring. This year, however, its ice cover is almost average for the time of year according to the Cryosphere Today regional SIA graph:

The Bering Sea region is above average and will hit its maximum SIA fairly easily in the coming weeks:

But as we so often see in the Arctic, an increase in one part is countered by a decline in another part. The Siberian side of the Arctic is where we see a significant slowdown in ice formation this year. The freeze-up was slow anyhow because of relatively warm waters at the end of the melting season in the Laptev, Kara and Barents Seas. But where the Laptev Sea has frozen up alright, it seems a couple of cyclones in the past weeks have stirred things up enough for large expanses of water to stay open in the Kara and Barents Seas (white demarcations according to the CT division of regions):

This is reflected on the regional SIA graphs, showing some big anomalies:These Seas will probably reach their maximum ice cover in the months to come, but much of it won't be very thick. We'll have to wait and see what this will mean for the ice retreat on the Siberian side of the Arctic and the Northern Sea Route when the melting season gets underway again.

These maps are provided by the Baltic Sea Portal and show last year's situation (left), this year's situation (middle) and average (= normaali) ice conditions (1965-1986) on the right. 'Jäätä' means ice. This year there's still no ice whatsoever (see MASIE regional map), whereas last year the ice cover was way above average.

As Diablobanquisa explains this has a lot to do with the NAO (Northern Atlantic Oscillation). When the NAO is negative a weak high west of Europe makes for weak winds, lower temperatures and thus more ice. With a positive NAO it's the other way around: stronger high, stronger winds, higher temperatures, less ice.

This image from a paper by Timo Vihmaa and Jari Haapala in Progress In Oceanography illustrates the point:

Comments

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Thanks Neven.

Though you should exercise your psychic powers more vigorously. I spent a fair bit of time yesterday looking through a heap of these maps and graphs. If I'd 'received the message' that you were doing the job for me, I could have saved a bit of time.

Thanks for another interesting post Neven. My post on methane will be delayed, my internet/phone failed before Christmas and I'm only just back on, then I start work again next week. I'm also wrestling with a recent paper about bifurcations in Arctic sea-ice - Abbot/Silber/Pierrehumbert "Bifurcations leading to summer Arctic sea ice loss."

Thanks, I should have linked to the copy - it's where I got mine from.

Another key point is that during the transition to a seasonally sea ice free (what we're seeing now), tipping points are less likely than for the next transition , to a perennially sea-ice free state. That result is common to Eisenman & Wettlaufer who find tipping points more likely in the transition to a perennially ice free state.

At the risk of making my blog post superfluous: Another relevant paper is Abbot & Tziperman "Sea ice, high-latitude convection, and equable climates."http://geosci.uchicago.edu/~abbot/PAPERS/abbot-tziperman-08a.pdf
It's a paper that I find scary.
"...the [perennially] ice-free state is stable for values that may be reasonable for the Arctic ocean during the late Cretaceous and early Paleogene (OHT = 0, CO2 = 250–2000 ppm,AHT = 80–100% modern)."
OHT = Ocean heat transport.
AHT = Atmospheric heat transport.